The present disclosure herein relates to a signal processing system, and more particularly to, a signal processing apparatus that decreases the effect of noise in a sensor generated according to the analog to digital conversion of a signal received from a plurality of sensors, and a method of controlling clock according to analog to digital conversion thereof.
A signal processing apparatus converts an analog signal received from a plurality of sensors to a digital signal for signal processing. In this case, the plurality of sensors may be sensors that sense biometric signals at medical devices, for example. These sensors include sensors for measuring magnetocardiography (MCG), magnetoencephalography (MEG), electrocardiography (ECG), electroencephalography (EEG), etc. sensors, for example. For example, one of these sensors is a superconducting quantum interference device (SQUID) sensor.
The signal processing apparatus uses an analog to digital converter (ADC) for the digital conversion of an analog signal from the SQUID sensor. A plurality of ADCs may be used due to a plurality of channels, a common digital clock frequency is used for the operation of all ADCs, and the output of the ADCs is transmitted in series or in parallel.
When the plurality of SQUID sensors operate in a magneticallay shielded room and an ambient high-frequency electromagnetic signal is generated, the SQUID sensor receives the effect of the signal and thus the function of the SQUID sensor decreases. In particular, the high-frequency digital clock signal used when converting an analog voltage signal into a digital signal may significantly decrease the performance of the SQUID sensor, as described above. Thus, in a structure that uses a plurality of ADCs or in a structure that uses the common digital clock frequency, the SQUID sensor experiences an increase in noise of a digital signal or beating due to a clock signal overlap or a phase difference. An increase in high-frequency clock noise in the SQUID system that measures a weak magnetic field decrease system due to inflow into the SQUID performance and since the beating generates low-frequency noise, there is a limitation in that it is difficult to precisely measure a magnetic field in a low-frequency region.